The ink jet recording method performs recording of images or letters by allowing ink droplets ejected by various working principles on a recording sheet such as paper. Ink jet printers have such favorable features that they make high-speed recording possible, that they produce little noise, that there is no limitation as to kind of patterns or images, and that it requires no processing for development and fixing, and attract attention in that they can accurately and quickly produce complicated images. Especially, the ink jet printers are rapidly becoming widespread in various fields as devices for producing hard copies of image information such as letters and various graphics produced by computers. Furthermore, they can easily perform multi-color recording by using a plurality of ink nozzles. The images formed by the multi-color ink jet recording method are comparable to those printed by a multi-color press or those obtained by a color-photography. Besides, use of the ink jet recording extends to a field of full-color image recording where the number of copies is not so many, since costs per copy are less than those employing the photographic process. The application fields of particular notice recently are production of color mechanicals in the printing industry, production of full-color copies of graphics in the fashion or promotion industries, and so forth. An another expanding field of note is transparency for OHP (overhead projector); color copies of a picture, graph, chart and the like drawn by aid of a computer are ink-jet printed and increasingly used for presentations.
As for the recording sheets used for ink jet recording, efforts have been made from the aspects of printer hardwares or ink composition in order to use woodfree paper or coated paper used for ordinary printing or writing. However, improvements in recording sheets have come to be required increasingly in order to go side by side with developments in printer hardwares such as ever increasing speed, development of ever finer definition images of full color, and also with expanding fields of uses. That is, recording sheets are demanded to develop ever high image reproducibility, and in order to meet that demand, it is required that image density of the printed dots be maintained high and hue characteristics be bright and appealing, the ink applied be fixed quickly and does not bleed or spread even though a different color ink is put over additionally. Moreover, ink should set quickly, dots should not spread more than needed and the circumference of dots be sharp and demarcating. Especially, in the case of color recording, not only the monochromatic recording of yellow, magenta, cyan or black is carried out, but also recording by overlapping these colors is carried out and amount of ink applied to the recording sheet further increases and very severe performances of the sheet are required.
When a conventional ink absorbing layer is provided on the recording sheet which is used for OHP, that layer--if porous, blocks light transmission of the sheet even if a transparent support is used; if non-porous, light transmission may be improved, but aqueous ink receptivity of the layer is poor, therefore ink remains wet on the surface of the sheet and printed image tends to be smudged during the time the sheet is run on a printer.
For solution of these problems, various ink jet recording sheets provided with a transparent ink absorbing layer high in ink receptivity have been proposed. For example, there have been proposed use of polyvinyl alcohol and polyacrylic acid type water-soluble polymer in Japanese Patent Application Kokai No. 60-168651, use of hydroxyethylcellulose in Japanese Patent Application Kokai No. 60-262685, use of a mixture comprising carboxymethylcellulose and polyethylene oxide in Japanese Patent Application Kokai No. 61-181679, use of a mixture comprising a water-soluble cellulose and polyvinyl pyrrolidone in Japanese Patent Application Kokai No. 61-193879, use of a receiving layer formed of a gelatin solution having a specific pH in Japanese Patent Application Kokai No. 62-263084 and use of a mixture comprising gelatin and a surface active agent in Japanese Patent Application Kokai No. 1-146784.
The ink jet recording sheets described in these patent applications are superior in light transmission and improved in ink receptivity, but are still insufficient, especially in dots reproducibility, and are hardly acceptable as recording sheets for high image quality color hard copies.
The object of the present invention is to provide ink jet recording sheets which give excellent quality images.
An aqueous ink to be used for ink jet recording is composed mainly of water and a polyhydric alcohol, and is designed to inhibit plugging of ink conduits or nozzles in the printer head and to improve discharging characteristics. I order to develop high quality image, it is necessary that ink-receiving layer can quickly absorb the ink and can control spreading of the ink.